Repellents are substances having a repellent effect on insects or arthropods. Their use in human and veterinary hygiene is of great practical importance, where they protect man and beast against attack by bloodsucking, biting or otherwise annoying insects. It is required that repellents, which are directly applied onto the skin or fur, are well tolerated, non-toxic, perspiration-resistant and light-fast and perfect in cosmetic respects. Moreover, the protection of the treated areas should last for the longest possible period of time and the spectrum of activity should be as broad as possible, i.e. they should act against the largest possible number of harmful and annoying insects by repelling them.
In the past, essential oils such as citronella oil, camphor and eucalyptus oil have been used as natural repellents; however, due to their perceived disadvantages they were predominantly replaced by synthetic repellents, such as phthalic acid dimethyl ester, 1,2-ethyl hexane-1,3-diol, 3,4-dihydro-2,2-dimethyl-4-oxo-2H-pyran-6-carboxylic acid-n-butyl ester, succinic acid dipropyl ester, N,N-diethyl-3-methyl-benzoic acid amide, pyridine-2,5-dicarboxylic acid-d-n-propyl ester, etc. However, such synthetic repellents are often not perspiration-resistant and/or irritate the mucous membranes and skin and, more recently, some have been determined not to be bio-degradable.
Use of repellants is regulated in the United States by the Environmental Protection Agency (EPA) under authority of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). To protect the public, the environment, and natural resources, repellants for all applications must be registered, unless they contain only ingredients that are specifically “exempt” from the registration requirements of the EPA. These exceptions or exemptions are updated from time to time and current lists may be obtained from the Environmental Protection Agency. Products containing exempted active ingredients and permitted inert ingredients are not required to satisfy the more rigorous registration requirements of FIFRA if contained on the above-mentioned lists. Such EPA exempt repellant products are highly desirable due to their safety profile and lack of persistence in the environment. Unfortunately, there is not guidance regarding how such listed ingredients may be used or combined to provide synergistic or even commercially economic effects.
Various insect pests, such as flying insects, including but not limited to arthropods (i.e. mosquitoes, noseeums), gnats and flies (house flies, black flies, horse flies, etc.), ticks and mites are a nuisance and may pose a health risk to humans, pets and other domesticated animals, particularly when the humans or animals are in outdoor environments. One attempt to reduce the nuisance and risk factors associated with such insect pests involves the use of various control or application means (e.g., topical repellants) for keeping various insect pests from flying or crawling near/on, stinging, biting, harming or otherwise annoying humans, pets and other domesticated animals. For instance, insect repellant compositions can be used in clothing, furniture, foodstuffs, or can be used nearby humans or animals, such as in candies or sprays to repel insect pests.
It is known that compositions derived from organic material, such as plant “essential oils” (e.g., oils produced from various plants & plant parts) have also been shown to have insect repellant and/or insecticide activity. Compounds isolated from plant essential oils as well as derivatives of these isolates have also been shown to have repellant or insecticidal activity. In today's market there are a number of plant essential oils being marketed to repel insects or animals. Plant essential oils tend to be volatile and will evaporate quickly when exposed to the elements. In many cases these essential oils are dissolved in mineral oil both to lower the cost and extend the useable life of the essential oil after it has been applied and exposed to the elements. The mineral oil acts as a carrier and a binder in this case and will greatly slow the evaporation of the essential oils. In addition, while many natural or organic based repellant compositions have been identified, highly effective compositions and formulations using such non-synthetic materials has not been known. Both synthetic or natural insecticides and insect repellants can be applied directly to a subject (i.e. topical application in creams, sprays or lotions), but may also be used with a variety of application systems (sprayers) to either kill or repel insects. Depending on the nature of the active ingredient, topical application may not be desirable as it can irritate the skin of the subject.
N,N,-diethyl-m-toluamide (“DEET”) is the active ingredient found in most commercial topical insect repellents. The current U.S. Army insect repellent (EDTIAR) contains DEET as its active ingredient. DEET is a derivative of toluene, an organic solvent, and is regarded as a highly-effective biting-insect repellant yet discovered. How well DEET works depends on the concentration in which it's applied. Low-strength formulations containing 12.5% DEET are 60-75% effective. High-strength formulations containing up to 100% DEET can be 95%+effective for over 4 hours on blackflies (Simulium spp.) and up to 10-12 hours on mosquitoes (e.g., Anopheles, Culex pipiens, and Aeges aegypti). It is also somewhat effective in repelling ticks, chiggers, punkies, and noseeums. The major commercial brands, Off!®, Deep Woods Off!®, and Cutter®, are DEET based products and comprise a vast majority of insect repellent sales. Products with the highest concentration of DEET last the longest against mosquitoes, but excessive use of DEET is believed to pose some risk, especially for children. Other disadvantages associated with DEET include: it is a synthetic chemical having a limited spectrum of activity and a noticeably unpleasant odor; it is a powerful plasticizer and will dissolve or mar many plastics and painted surfaces; it plasticizes inert ingredients typically used in topical formulations in order to lengthen the time of effectiveness. As a result, DEET formulations have low user acceptability.
Desirable properties of a topical insect repellent include low toxicity, resistance to loss by water immersion or sweating, low or no odor or at least a pleasant odor, ease of application, and rapid formation of a dry tack-free surface film. Attempts to improve the properties of DEET through polymer or microcapsule formulation have been frustrated by DEET's plasticizing properties, which lead to a high tack skin surface. Further, efforts to develop a natural insect repellent have motivated studies of oils of citronella, turpentine, pennyroyal, cedarwood, eucalyptus and wintergreen, but these are relatively ineffective (see, e.g., Handbook of Nonprescription Drugs, 1993, 10th Ed., American Pharmaceutical Assn., Washington, D.C.). Some reports have indicated that “natural products” and products that do not contain DEET provided little or no protection against mosquitoes. Further, insect repellents for nonprescription oral use are not generally recognized as safe and effective (Federal Register, 1985, 50: 25170).
Clearly there is a need for a long-lasting effective insect and arthropod repellent that is pleasant to use and that will not damage plastic containers, or the text printed on the containers. Other desirable attributes include at least the following:                Formulations that contain no DEET        Safe around children and pets        Repel mosquitoes and ticks        Non-greasy and non-staining        Low odor        Works as well as or better than conventional DEET formulations        